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Remove old unused kernels from Red Hat Enterprise Linux 5 & Fedora 12/13
Install using yum install yum-utils Options include: --oldkernels Remove old kernel and kernel-devel packages --count=KERNELCOUNT Number of kernel packages to keep on the system (default 2) use package-cleanup --help for a complete list

Remove all the files except abc in the directory
Finds all files in the current directory and deletes them besides file called "abc"

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

find duplicate messages in a Maildir
# find assumes email files start with a number 1-9 # sed joins the lines starting with " " to the previous line # gawk print the received and from lines # sort according to the second field (received+from) # uniq print the duplicated filename # a message is viewed as duplicate if it is received at the same time as another message, and from the same person. The command was intended to be run under cron. If run in a terminal, mutt can be used: mutt -e "push otD~=xq" -f $folder

Convert (almost) any video file into webm format for online html5 streaming

Remote backups with tar over ssh
Execute it from the source host, where the source files you wish backup resides. With the minus '-' the tar command deliver the compressed output to the standar output and, trough over the ssh session to the remote host. On the other hand the backup host will be receive the stream and read it from the standar input sending it to the /path/to/backup/backupfile.tar.bz2

Big Countdown Clock in seconds
Requires figlet. Other than that, this should be portable enough across all the Bourne-compatible shells (sh, bash, ksh, zsh, etc). Produces a massive number using figlet that counts down the number of seconds for any given minute interval. For example, here's a 4-minute timer: $ i=$((4*60)); while [ $i -gt 0 ]; do clear; echo $i | figlet; sleep 1; i=$(($i-1)); done; And a 1-minute timer: $ i=$((1*60)); while [ $i -gt 0 ]; do clear; echo $i | figlet; sleep 1; i=$(($i-1)); done;

Mount a Windows share on the local network (Ubuntu) with user rights and use a specific samba user

Start a terminal with three open tabs
If you launch gnome-terminal manually, you can start with three open tabs

Pick a random line from a file
This is from perldoc -q random.*line, which says: This has a significant advantage in space over reading the whole file in. You can find a proof of this method in The Art of Computer Programming, Volume 2, Section 3.4.2, by Donald E. Knuth. Who am I to argue with Don Knuth?


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